Quantifying acetylene mole fraction in rich flat laminar premixed C2H4/air flames using mid-infrared polarization spectroscopy

• Published in: Applied physics. B, Lasers and optics Lasers and optics, 2023-08, Vol.129 (8), Article 120
• Main Authors: Zhao, Wanxia, Alwahabi, Zeyad T., Dally, Bassam B.
• Format: Article
• Language: English
• Subjects: Acetylene; Applied physics; Collisional broadening; Engineering; Gas temperature; Infrared lasers; Infrared spectroscopy; Ions; Lasers; Optical Devices; Optics; Photonics; Physical Chemistry; Physics; Physics and Astronomy; Polarization; Quantum Optics; Scaling factors; Soot; Spectrum analysis
• ISSN: 0946-2171; 1432-0649
• DOI: 10.1007/s00340-023-08065-0

Mid-infrared laser polarization spectroscopy (IRPS) has been applied to measure the mole fraction of acetylene in rich premixed laminar C 2 H 4 /Air flat flames at equivalence ratios ( Φ ) of 1.7, 2.1, and 2.3, and under atmospheric pressure. The detection was conducted by probing the ro-vibrational P(19) transition at ~ 3.1 μm. The total collisional broadening coefficient of C 2 H 2 was approximately 0.074 cm −1  atm −1 and varied within a range of 0.5% under different flame conditions, which made the effect of linewidth not obvious in the CH 4 /air flame. The calculated mole fraction of C 2 H 2 , using the Chemkin model, at Φ  = 1.3 and 1.5 was used to calibrate the recorded IRPS signal intensities at different Height Above Burner (HAB). A single scaling factor was then used to quantify the measured C 2 H 2 at highly sooting conditions, Φ  = 1.7, 2.1, and 2.3, with a Limit of Detection (LoD) of 35 ± 5 ppm. The first observed C 2 H 2 mole fraction appeared at HAB of 3 mm and measured as 2003 ppm, 2217 ppm, and 2495 ppm, for Φ  = 1.7, 2.1, and 2.3, respectively. The mole fraction increased as the HAB increased to reach the maximum value of 2296 ppm, 2807 ppm, and 3478 ppm, for Φ  = 1.7, 2.1, and 2.3, respectively, up to HAB of 5 mm. It was observed that the C 2 H 2 mole fraction reaches a plateau region at HAB of ~ 8 mm. The production of C 2 H 2 has been observed to be subject to a critical gas temperature of 1400 ± 30 K. The critical soot inception temperature, where the first incepted soot particles are observed, is the same as the gas temperature where χ C 2 H 2 max was detected, namely at 1500 ± 30 K. These measurements and calibration procedure demonstrate a plausible technique to probe other flames and to better understand soot inception and its correlation with C 2 H 2 .